This invention relates to correction fluids of the type used for obscuring indicia on sheet material.
During the 1950s, Mrs. Bette C. Graham developed a correction fluid to cover and obscure typing errors. Although her exact formulation was maintained secret, it was known to contain a pigmented thermoplastic polymer or resin dissolved in a volatile solvent. An error was corrected by brushing the correction fluid over it and allowing the solvent to evaporate.
Although the basic components (solvent, polymer, and opacifying pigment, especially rutile TiO.sub.2) have been used in almost all correction fluids since the time of Mrs. Graham, the individual components have been varied and certain additives included to improve performance. For example, U.S. Pat. No. 3,276,870 discloses the use of such solvents as methylethylketone, methyl alcohol, benzene, ethyl acetate, and preferably toluene, and U.S. Pat. No. 4,165,988 suggests the use of a solvent mixture comprising methyl chloroform and perchloroethylene. U.S. Pat. No. 3,997,498 proposes fluorochloroethanes as solvents for resins such as poly(n-butyl methacrylate), isobutyl methacrylate:n-butyl methacrylate copolymers, poly(isobutylmethacrylate), alkyds, coumarone-indene resins, poly(styrene) resins, butadiene-styrene copolymers, and vinyl ethers. The previously mentioned U.S. Pat. No. 3,276,870 suggests as resins a polyester formed by reacting sebacic acid and glycol, the catalyzed reaction product of monomeric dienes and reactive olefins, orange shellac, cellulose acetate, vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, and, apparently preferably, methyl acrylate-methyl methacrylate copolymer.
The correction fluid of aforementioned U.S. Pat. No. 3,997,498 is said to be effective in obscuring not only typewritten indicia but also electrostatically reproduced indicia in which copies are based on pigmented toner resin. (It is curious that the amount of pigment present in this correction fluid is said to constitute from 15 to 35 weight percent of the solids, or perhaps somewhat less, considerably lower than in commercial correction fluids.) Notwithstanding the disclosure of this patent, manufacturers presently provide three specific types of correction fluid, one for typewritten material, one for electrostatic copies, and one for writing ink, employing a different organic or water-based solvent system for each to avoid dissolving or smearing the specific indicia to be covered.
Most correction fluids are supplied in a small bottle with an applicator brush attached to the cap. Since the opacifying pigment tends to settle out during use, glass or metal mixing beads are often included to help redisperse the pigment, the user being instructed to shake the bottle prior to application of the correction fluid. Unfortunately, thorough shaking is commonly regarded as a nuisance, so that much of the pigment remains at the bottom of the bottle. This condition is exacerbated by the fact that the solvent tends to evaporate when the bottle is open; although replacement solvent is available, it is rarely used. As a result, much of the correction fluid in each bottle is thrown away as the solids become increasingly difficult to disperse.